The forest diggers

Walk a patch of gum forest or wallum at first light, after a still night, and you can read what happened in the dark without ever seeing the animal that wrote it. Small conical holes dimple the forest floor, each the size of a snout, punched neatly into the litter like the ellipses of an unfinished sentence. Something has been working the ground while the forest slept. That something is one of the coast’s most important animals, and one of its least seen: a small, snuffling, night-digging marsupial, going quietly about a job the whole forest leans on.

To understand the job you have to start underground. Nearly every tree and shrub on this coast feeds a fungus at its roots and is fed in return, the mycorrhizal partnership without which these starved soils would grow very little. Many of those fungi, though, fruit not as toadstools out in the open air but as truffle-like bodies sealed below the surface, and a fungus underground has the same trouble as a plant rooted to the spot: it cannot move its own spores. So it does what the plants do. By courier, paid in food.

The couriers are a guild of small marsupials with a nose for buried fungus and the claws to reach it. On the Sunshine Coast these are the bandicoots, the still-common northern brown bandicoot (Isoodon macrourus) and the long-nosed bandicoot (Perameles nasuta), and, more localised and more fragile, the long-nosed potoroo (Potorous tridactylus), a rabbit-sized cousin of the kangaroos. The potoroos are the true fungus specialists here, much of their diet made of these hypogeous, or below-ground, fruiting bodies; the bandicoots take them more opportunistically, along with the grubs and roots they also dig for (Claridge & May 1994). (The rufous bettong (Aepyprymnus rufescens) belongs to this coast as well, though it has become scarce enough here that its diggings are far easier to find than the animal. It is the arid-country Bettongia bettongs, rather than bettongs as a group, that are the genuinely outback example.)

The animal sniffs out the buried fungus, digs it up and eats it, and the spores pass through its gut unharmed, to be dropped, still alive, somewhere new, in a neat parcel of its own fertiliser. In eating the fungus, the digger plants it. It is the underground version of a bird carrying a berry, and what it sows is the mycorrhizal partner the trees’ roots depend on.

And that is only half the animal’s night’s work. A bandicoot or a potoroo working the ground until dawn turns over an astonishing amount of soil: thousands of little diggings, each one loosening the crust, folding leaf litter into the earth, letting in water and air. Ecologists call this bioturbation, the low art of the plough. The animal is only feeding itself. The turned soil and the sown fungus come with it.

Take the digger away, and the forest does not fall over. It thins, slowly, from below. The fungal network frays. The trees that lean on it lose a little vigour, and the soil sets a little harder, a quiet unravelling almost nobody would trace back to a missing marsupial. Which is more or less what has happened across much of Australia. The digging marsupials sit squarely in the critical weight range, the band of small-to-medium mammals that the red fox and the feral cat find easiest to kill, and that has borne the worst of the continent’s mammal extinctions. Between them the two introduced hunters have pulled these animals down to scattered remnants, or wiped them out altogether.

The Sunshine Coast’s larger, better-protected bushlands still keep some of theirs, for now: a bandicoot crossing a track at dusk, a fresh field of diggings by morning. But their thinning draws one more thread softly out of the web, and it is a loss of a peculiar kind. It does not show at the surface. It happens down in the roots, where hardly anyone thinks to look, which is what makes the forest diggers so easy to lose, and so worth reading the ground for.